The present invention relates to a circular knitting machine for stockings, particularly for the manufacture of stockings closed at the toe directly on the machine.
For the closing of stockings, panty hose, men's socks or the like at the toe there is known a method including the formation of a double fabric at the toe, by withholding a part of the loops with selected needles in the upper needle cylinder of a double cylinder knitting machine or with the hooks of the welt dial in the case of a single cylinder machine, and forming with the needles in the lower needle cylinder a pocket which is then subjected to a torsion by means of a temporary rotation of the lower needle cylinder relative to the upper needle cylinder or to the welt dial before bringing back to the lower needle cylinder the loop withheld so as to form a double fabric tightened at the toe.
The most relevant problem in this case is felt when having to carry out the relative rotation between the cylinders of the machine or between the lower cylinder and the welt dial in a rapid and precise manner so as to have the grooves of the needles perfectly aligned in both cylinders for the execution of the subsequent step even after the relative rotation of the cylinders.
In order to carry out the above mentioned relative rotation, at present it is customary to stop the upper needle cylinder or the welt dial while the rotation of the lower needle cylinder continues. For this purpose, there is provided a coupling between the drive shaft and the gear wheel which meshes with the corresponding crown gear rigid with the upper cylinder or welt dial so that the above mentioned gear wheel may axially slide on the shaft and be disengageable from the crown gear of the upper needle cylinder or welt dial. The frequency with which the operation of engagement and disengagement must be carried out for each stocking or the like and the stresses which arise each time, give rise to a fast wear of the mechanical coupling means, particularly between the gear wheel and the drive shaft. This fact together with the limited coupling surfaces and their closeness to the rotational axis, causes large alignment errors between the needles even in the case of small degrees of wear of the coupling means, with disastrous results for the machine itself.
According to another solution, the gear wheel meshing with the gear crown of the upper needle cylinder is not axially displaceable on the drive shaft but is mounted axially not displaceable and rotationally idly on the same shaft and there is provided a sleeve member axially slidable along the shaft and rotationally connected to it. This sleeve member has one or more teeth insertable in corresponding slots arranged angularly spaced on a body rigid with the gear wheel. The axial displacement of the sleeve member, which displacement causes the disengagement and engagement between the teeth of the sleeve element and the slots of the gear wheel and therefore between the drive shaft and the gear wheel, is operated by means of a lever system controlled by the machine program.
Even this solution is not however free of the drawbacks mentioned for the preceding solution, since the coupling between the sliding sleeve member and the drive shaft nevertheless occurs between small coupling surfaces and very close to the rotational axis with the consequences already mentioned.